1. Field of the Invention
This invention relates to a pressure vessel of an X-ray detector, and more particularly, this invention relates to the structure of the window portion of a vessel of an X-ray detector.
2. Description of the Prior Art
X-ray detectors are used in computer-tomographs which are widely used in the medical field. The conventional X-ray detector of this kind comprises a container of a curved pillar shape. The container is usually made of an aluminum alloy. The container has a window facing the inside curvature of the container. X-rays from an object pass through the window. A carbon fiber-reinforced plastic (hereinafter referred to as CFRP) sheet is attached to the inner wall of the periphery of the window by means of an epoxy resin-based adhesive so as to gas-tightly cover the window. The container is filled with a gas such as xenon, which is opaque with respect to X-rays. The pressure of the gas in the container is usually 10 to 50 atms. The gas is ionized upon impingement of X-rays, and the intensity of the impinged X-rays is determined based on the degree of ionization of the gas. A plurality of parallel planar anodes and a plurality of parallel planar cathodes are alternately disposed in the container to form a number of cells. The intensity of the X-rays impinging on each cell is determined and computer-analyzed to form an image of an object.
Some conventional X-ray detectors further comprise an aluminum foil of about 50 .mu.m thickness attached to the inside of the CFRP sheet. The aluminum foil serves to compensate for the brittleness of the CFRP sheet and to shut out an organic gas which may be generated from the CFRP upon impingement of X-rays. A contact potential difference arises between the CFRP sheet and the aluminum foil. The potential difference is increased by amine groups in a hardening agent in the epoxy resin-based adhesive. Due to the potential difference, the aluminum foil is corroded, so that thin through holes are formed in the foil. As a result, organic gas from the CFRP sheet diffuses into the container to contaminate the xenon gas in the container. As a result, the insulation property of the xenon gas is reduced, so that the detection accuracy is degraded.